The purpose of the proposed studies is to examine the effects of aging on hormone-sensitive adenylate cyclases of rat liver. In vitro systems will be used to study four aspects of catecholamine- and glucagon-sensitive liver adenylate cyclases as function of age. Firstly, age-related alterations of hormone-sensitive adenylate cyclase activities will be monitored. Secondly, the mechanisms of aging changes of adenylate cyclase activities will be explored by examining individual components of the enzyme complex (hormone receptors, guanine nucleotide regulatory component, and catalytic component) as a function of age. The effects of aging on modulators (cytosol protein activator(s), cations, anions) of adenylate cyclase activity will also be studied. Thirdly, studies of the effects of aging on other plasma membrane-bound enzymes (ATPases, 5'-nucleotidase) as well as plasma membrane lipid composition and fluidity will be conducted to determine if aging changes of adenylate cyclases reflect alterations of the plasma membrane. Finally, the role of diet in age-related alterations of adenylate cyclase activities will be examined. These studies should provide specific information about regulation of the hormone-sensitive adenylate cyclase enzyme complex and general insights into aging a physiological determinant of hormone action at the plasma membrane.